How to Measure Ring Size at Home: A Jeweller's Guide

Ring size is the one detail of a ring you cannot judge from a photograph, and the internet is full of confident charts that quietly disagree with each other. As jewellers who size and resize rings at our own bench, we spend a surprising amount of time undoing measurements that were taken at home with great care and the wrong tools.

So here is the honest version: the chart Australian jewellers actually work to, the methods that work, the methods that only half work, and the point at which you should stop measuring and let a jeweller put metal on your finger.

How do you measure ring size at home?

The most reliable way is to measure a ring the wearer already uses on that exact finger: read its inside diameter against the chart below, or bring it to a jeweller. A strip of paper or string around the finger gives a rough circumference to check against the same chart. When the two disagree, or you sit between sizes, size conservatively.

Each method has a proper technique and an honest margin of error, so it is worth understanding what each one can and cannot tell you before you order a ring around the result.

Australian ring size chart (mm and US sizes)

Australia sizes rings on the same alphabetical scale as the United Kingdom, set by British Standard BS 6820. Size C has an inside circumference of 40 mm, and every full letter adds 1.25 mm, so a half size adds 0.625 mm. The chart covers the sizes we fit most often at the bench.

Read the circumference column if you measured the finger with string or paper, and the diameter column if you measured across the inside of a ring that already fits. The US column is the nearest quarter size for rings bought from North American sellers.

Method one: measure a ring that already fits

A ring that is already worn on the target finger is the best measuring tool that exists outside a workshop. Lay it on a ruler and read the inside diameter, edge to edge across the middle, then find the nearest row in the diameter column. Better still, bring it in and we will read its size on a mandrel, or trace the inside of the ring on paper if the ring itself cannot travel.

Two details decide whether this method works. First, the ring must come from the same finger of the same hand; a ring from the right hand will mislead you, and a ring from a different finger of the left hand will mislead you more. Second, width matters: a wide band needs a touch more room than a fine one on the same finger, so tell us how wide the new ring will be when you hand over the measurement.

Method two: the string or paper strip method

Wrap a thin strip of paper, or a piece of string that does not stretch, snugly around the base of the finger, mark the exact point where it overlaps, and measure that length against a ruler in millimetres. That length is the finger's circumference: find the nearest figure in the circumference column of the chart to read the size.

Treat the result as an estimate, not an answer. String stretches, paper kinks, and pulling the strip a little tighter or looser changes the reading by more than a full size, which on this scale is only 1.25 mm. The ring also has to pass over the knuckle, not just sit at the base of the finger, which is exactly the kind of judgement a sizing gauge at the bench settles in seconds.

Printable charts and sizing apps: the honest caveats

Printable ring sizers and phone apps share one flaw that no amount of care fixes: paper scale and screen scale lie. A chart printed at slightly the wrong zoom, or a circle displayed on a screen with different pixel density, will hand you a confident and wrong answer.

If you do use a printable chart, check its own scale reference against a ruler before trusting anything else on the page, and cross-check the result against a ring that already fits. Whenever the chart and the metal disagree, trust the metal. We would rather see the ring than the printout.

How do Australian ring sizes convert to US and European sizes?

Australian, British and New Zealand jewellers use letters; North America uses numbers in quarter steps; much of Europe simply quotes the inside circumference in millimetres. Because the Australian scale is defined by circumference, the circumference column above doubles as the European size: an Australian K is 50 mm, which a European seller calls a 50.

Conversions are close but not perfectly aligned, because a US quarter size and an Australian half size are slightly different steps. When you order from overseas and the size sits between two numbers, choose the conservative option and confirm with a jeweller before anything is set.

When should you get measured professionally?

Before any ring that cannot easily be resized, and whenever the methods above disagree. Walk-ins are welcome in opening hours at our Cottesloe atelier, an appointment holds a jeweller's time, and a size taken on the metal beats every chart, app and string measurement made at home.

Timing matters more than people expect, because fingers change with heat. In Perth, a size taken on a cold morning can feel tight in February, and we allow for that at the bench. If you are commissioning a ring, a professional fitting also lets us match the size to the band's width and profile rather than to a bare number.

The conservative size rule

When you are caught between two sizes, or you are not fully sure of the measurement, size conservatively. A ring that is slightly small is easier to live with for a week than one that spins off at the sink, and it gives the jeweller clean metal to work with when the final adjustment is made.

That works because resizing is routine at a proper bench: we resize in our own Cottesloe workshop, including rings we did not make, and most modern rings can move a size or two without drama. The exceptions are worth knowing before you buy: some antique shanks, tension settings and fully set eternity bands have tighter limits, and a plain shank is kinder to later adjustment than a band paved all the way around.

Sizing a ring for someone who must not find out is its own game, from borrowed rings to discreet invoices. For that, read How to Size a Surprise Ring in Perth before you guess.